I power an amplifier using ADD-55 power source with "built in UPS functionality". As supposed, it charges a battery connected to "battery" output, and continues to run on it when mains power fails.
What I don't understand is why power source doesn't start on that battery. I.e. I have a spare charged battery "in the field", no mains power, and I want to switch on the amplifier. Unexpectedly, the only way to start without mains power is to connect a battery to +V output of power source (not "battery" output).
What is proper way to arrange such a cold start?
Addition: power source is ADD-55A, load is custom built RF amplifier, battery is lead-acid 12V 3A*h, circuit is trivial: